may mean different aircraft manuals have different soft field techniques.
Surely they’ll be in the POH?
Scenic_Flyer wrote:
Some mixed theories here concerning the relative amount of drag being produced by the elevator… hmm. I read in my aa5 poh that using a full yoke back technique increases your TORR because you’re basically doing a wheelie, thus creating a higher alpha on the wing which in turn increases drag. Makes sense right?
Basically, yes, but you just start your soft field takeoff roll with full deflected elevator and reduce back-pressure when the nosewheel is lifted. You want to keep it just barely above the ground until you have sufficient speed to lift off with an additional pull of the yoke, if necessary. It is the same principle that let’s you begin your crosswind takeoff roll with full deflected ailerons into the wind and reducing as they develop “grip”.
Jan_Olieslagers wrote:
Surely they’ll be in the POH?
Not necessary. On elder aircraft you often just read a statement “Use the usual procedures” or “This airplane acts normal” or something similar. Those were the times the manual was written for aviators, not for lawyers :-)
Those were the times the manual was written for aviators, not for lawyers
That was perhaps before my time…
Scenic_Flyer wrote:
I read in my aa5 poh that using a full yoke back technique increases your TORR because you’re basically doing a wheelie, thus creating a higher alpha on the wing which in turn increases drag. Makes sense right?
That really makes sense! But: In case of a soft runway that extra lift will reduce the weight on your wheels and proportionally their drag, which in this phase of takeoff is a lot higher than the drag produced by the wing.
Maoraigh wrote:
Drag caused by the elevator down force on the tail forcing the main wheels into the mud, rather than lifting the noewheel and tilting the wing to produce lift?
Overall the downforce of the elevator is beneficial. The extra lift from the higher angle of attack outweighs the downforce onto the main wheels by an order of magnitude. High school physics is sufficient to do the calculation. You need to get the weight off the main wheels (which typically carry 90 percent of the mass of the aircraft) as fast as possible to reduce their drag. Only lift can do that and lift comes from speed and alpha.
Scenic_Flyer wrote:
I read in my aa5 poh that using a full yoke back technique increases your TORR because you’re basically doing a wheelie, thus creating a higher alpha on the wing which in turn increases drag. Makes sense right?
Yes, and I often do the same thing in my tricycle gear plane on landing, to reduce landing distance without using the wheel brakes. After landing on the main gear the nose can be held off until quite a low speed, and supporting (part of) the weight of the plane with the wing at high-ish AoA absorbs more energy than the rolling friction of the wheels supporting the same weight on a paved surface. I then use the wheel brakes as required after the nose wheel is on the ground.
I take off from softfields a lot, one of my main airfields is a Czech glider field with a pretty uneven runway, length is 650 Meters. I always pull back completely on the first meters orf the t.o. run, but of course I relax the back pressure once the elevator becomes effective. And one the wheels have left the ground I accelerate in ground effect in maybe only one meter AGL …
With the SR22 it is essential to protect the nosewheel, more so than im my Warrior, because the engine is much heavier and I think the nosegear is more delicate anyway. A nose gear failure in the landing or take-off run will produce an invoice of € 70 K, minimum, so there’s good reason to be careful …
I believe there is a specific technique for the Twin Otter for gravel strips found in Alaska/Northern Territories. The aircraft lifts off with flaps below V2 take off safety speed but then is accelerated in ground effect to Vxse. Getting the nose gear off the ground is probably a good idea unless you want to explore nose dragging as a concept. The nose gear digging in is a much higher drag factor than the elevator. Leaving ground effect with too high an AoA is what causes mushing accidents – the art is to accelerate in ground effect.
The big single engine tail wheel use flap to full right aileron deflection (assumes clockwise propeller) to minimize torque effect on the left gear (crosswinds notwithstanding), and should work for a twin unless it has c/r engines.
This topic is a bit too broad to have one correct answer. So, as few points (all in the context of tricycle airplanes):
With only a few exceptions, I will begin my takeoffs with full nose up pitch control applied. Once the nosewheel lightens, I’ll relax, and hold that position until liftoff, once off, I’ll allow the plane to accelerate close to the runway as appropriate. I find this technique most universally appropriate. It is more like a soft field than a short field, but it’s pretty rare that you need the full short field capability of an aircraft. The use of soft field technique will reduce wear and tear on landing gear, nosewheels in particular. The use of soft field technique also allows you to ease into the air, and ease into a possible crosswind, rather than suddenly thrusting yourself into it by suddenly “rotating”. If you don’t like the way the plane feels, or a drift which develops in a crosswind, an abort is still possible.
Yes, the up elevator will add drag to the takeoff run. However, for my experience, not so much that it will disallow a a takeoff which was a good idea anyway.
The exception I have learned (nearly the hard way) is T tailed Pipers, they should be rotated at the stated speed. If you hold full nose up through the takeoff roll, it’s going to jump up at some point, and startle you.
Arrows, like all Cherokees, do not have elevators, they have stabilators. A subtle difference, I know, but important if you’re going to drag the plane off the runway at a minimum speed. The stabilator can be stalled (a serious problem with the very first Cessna Cardinals). This is because the additional lift generated by the application of pitch up control is by AoA increase only (albeit upside down), rather than by a combination of AoA increase, and increased camber combined. I’ve stalled Cherokee stabilators a few times, and doing so can really prolong the takeoff run. Cessnas (other than Cardinals) do not suffer this. Indeed, you’ll find that with most 100 series Cessna tricycles, with 15 flap extended, and full nose up pitch control applied, the nosewheel can be lifted off the surface with high power, and nearly zero airspeed. Try with caution, as banging the tail is possible, and very undesirable.
Twin Otters are a little odd in this realm. Their flaps are enormously effective, and will pitch the plane nose down, so a whole bunch of up pitch control is needed to overcome this. That is coupled with the nosewheel steering being direct hand lever control, which is awkward. Getting the nose light, shifts the directional control to the rudder early, and the awkward nosewheel steering lever can be left centered. It s easy to wheelbarrow a Twin Otter, and/or “Station 60” damage it (which means break off the nosewheel).
If in doubt, keep the weight off the nosewheel as much as possible, unless you’re flying Tomahawks. As you know that you should control direction from the moment you open the throttle, to the moment you stop after the flight, ’same thing for pitch control!
There are a bunch of B-25s at Osh doing air shows. The speaker explained the procedure they perfected for carrier take offs, fully loaded. It was full aft trim, full flaps, then release brakes with stick in center. At the end of the deck, the stick was pushed hard fwd, then fully aft and held there until they started accelerating. With the trim in full aft position, this would give a “pogo effect” according to the speaker (nose wheel leg bouncing perhaps?) The only problem was when in the air, they were still 30 kts below min single engine speed, so if one engine stopped they would surely flip over and die.
